Using tree ring analysis to determine fire history in the Oklahoma Ozarks

W 2800.7 F293
T-46-P-1 12/06-12/11 c.1
FINAL PERFORMANCE REPORT
FEDERAL AID GRANT NO. T-46-P-1
USING TREE RING ANALYSIS TO DETERMINE FIRE
HISTORY IN THE OKLAHOMA OZARKS
OKLAHOMA DEPARTMENT OF WILDLIFE CONSERVATION
December 31, 2006 through December 30, 2011
FINAL PERFORMANCE REPORT
State: Oklahoma Grant Number: T-46-P-l
Grant Program: State Wildlife Grants
Grant Name: Using Tree Ring Analysis to Determine Fire History in the Oklahoma Ozarks
Grant Period: December 31,2006 - December 30, 2011
Principal Investigators: Richard P. Guyette, Michael C. Stambaugh, and Rose-Marie Muzika
Department of Forestry, University of Missouri
A. ABSTRACT:
The role of humans in past ecosystem fires has had little quantitative attention. Here, we address
this inadequacy by developing fire histories in northeastern Oklahoma at the Nature
Conservancy's Nickel Preserve from 324 dated fire scars on shortleafpine (Pinus echinata)
remnants and trees. The purpose ofthis study was to provide an understanding of the role of
humans, fuels, and climate in the historic fire regime. Variability in the historic fire regime was
associated with human population, time since last fire, and drought. The population density of
the Cherokee Nation and other Native American groups was significantly correlated (r = 0.84)
with the number of fires per decade between 1680 and 1880. At the Tully Hollow site the mean
fire interval (MFI) was 7.5 years from 1633 to 1731 and 2.8 years from 1732 to 1840. Before
1810, during low population densities of Osage and Caddo, the mean fire interval was 4.2 years.
Coincident with the removal of the Cherokee and other native peoples from the eastern United
States into northeast Oklahoma, the mean fire interval reached 1.8 years in length between 1840
and 1890 in this part of the Cherokee Nation. After 1925 a decrease in fire frequency (MFI = 16
years) occurred until the introduction of prescribed fire by the present owners (The Nature
Conservancy). Previously documented widespread (340 km east-west) fires that occurred during
drought years (1657, 1780, 1786 and 1808) in Missouri and Arkansas also occurred in the
Oklahoma Ozarks. Over all, the occurrence of fires at the study site was weakly associated with
drought years. During decadallength dry periods between 1680 and 1880 fire was less frequent.
Fire severity (as measured by the percent of trees scarred) appeared to be lessened in cases when
fire events were preceded by fires in the previous three years.
B. OBJECTIVE:
To determine the fire history of an oak-pine forest, woodland, and savanna mosaic in the
Oklahoma Ozarks, and to examine the key factors that historically influenced fire regimes in the
region.
C. INTRODUCTION:
Throughout North America the quantitative association of historic fire regimes with anthropo-genic
factors is often limited by the quality of data on Native American populations and to a
lesser extent their many cultures (Delcourt and Delcourt 1997). Rarely are human population
and culture data linked at the same location with long-term fire regime data. The Nature
Conservancy's Nickel Preserve in northeast Oklahoma was part ofthe Cherokee Nation in 1828
and it has a fire history that is strongly linked to human population, culture, and ownership for
over three centuries. Fire history information provides both perspective and baseline data that
are relevant to fire ecology, forest restoration, fuels management, human and ecological history,
and species distributions (Lafon 2005, Rudis and Skinner 1991).
The fire history of Oklahoma's diverse vegetation, landscapes, and people is beginning to be
described by studies conducted with fire-scarred oaks. Case studies using fire scar dates in oak
trees from east central (Clark et al. 2007, DeSantis et al. 2010) and southwestern Oklahoma
(Stambaugh et al. 2009) have begun to described the Cross Timbers region. These studies offer
managers with historic fire frequency information but are not often comparable because of site
differences. High spatial and temporal site variability has been found in fire frequency due to
topography, geographic location, and historic human occupancy. No previous-documented fire
histories are known to exist in the western Ozark Highlands region of Oklahoma. The nearest
Ozark fire histories are about 200 km east in higher, cooler, and wetter mountain environments
in northern Arkansas (Guyette et al. 2006). This study describes the historic fire regime in what
is now The Nature Conservancy's (TNC) Nickel Preserve in Cherokee County, Oklahoma by
using fire locations and dates as identified on fire-scarred remnants and trees.
D. APPROACH AND METHODS:
Study location
Study sites are located at what is presently the IT. Nickel Family Nature and Wildlife Preserve,
which occurs on the lands that were occupied by Native American tribes, and were assigned by
treaty to the Cherokee Nation in the decades before 1887 (Figure 1). The 6,880 ha preserve,
owned and managed by TNC since 2000, lies in the Cookson Hills of northeastern Oklahoma
and is bordered by the Illinois River to the west. The region lies on the western edge of the
Ozark Highlands with the lands further west occurring in the Cross Timbers physiographic
region (Clark et al. 2005). The climate is humid continental, with mean maximum temperatures
of22 "C and mean annual precipitation of 122 em. The topography is rugged and dissected, with
steep cherty slopes, ridges, and narrow valleys. Twenty to fifty percent of the region has slopes
over 14 percent (Rafferty 1980). Plant community associations include mixed oak-hickory
(Quercus sp.-Carya sp.) forests, mixed oak-pine (Quercus sp.-Pinus echinata Mill.) woodlands
and savannas, and small prairies.
Human history
The study site region has been continually occupied by humans throughout the period of the fire
scar record. During the early period (~1630-1830) of the fire scar record, the region was likely
occupied by the Osage and Caddo Native American groups (Vogt 1974). As early as 1541, the
study site was within the boundaries of the expanding Osage territory (Bums 2004) and other
Native American groups had left the region by the latter half of the is" century (Vogt 1974;
Bailey 2010). Osage villages were concentrated primarily in the Missouri and Arkansas Ozarks,
but they utilized the western plains portion of their territory for annual game and bison hunts.
The Illinois River trail was one of two significant trails utilized by the Osage for travelling from
Arkansas to Oklahoma hunting grounds (Bums 2004) that bordered the study site.
The Cherokees began migration and cultural change early (before 1775) in the east (Goodwin
1977). By 1817, the "Western Cherokees" that had been settling in Arkansas since the 1790s
were venturing into northeastern Oklahoma, encountering resistance from the Osage. Conflicts
continued between the two tribes through 1825 (Goins and Goble 2006). In 1828, a treaty led to
the exchange of Cherokee lands in Arkansas for land in Indian Territory encompassing the study
site after which the region was occupied primarily by Cherokee for more than 6 decades.
Between 1829 and 1838, the Western Cherokees were occupied with building cabins, clearing
land for cultivation, raising livestock and hunting bison (Jones and Faulk 1984). In 1838, most
of the remaining Eastern Cherokees were forced to relocate to northeastern Oklahoma on what
came to be known as the Trail of Tears. Approximately 5,000 Cherokee were already living in
lands west of the Mississippi when about 14,000 surviving emigrants from the East arrived
(McLoughlin 1993; Goins and Goble 2006).
Many emigrants arrived in the new territory destitute, and struggled to survive in an unfamiliar
climate and environment (McLoughlin 1993). The decades following the arrival of the Eastern
Cherokees were marked by much turmoil as the reunited tribe struggled to establish social,
economic and political stability (McLoughlin 1993; Goins and Goble 2006). Conflicts with
other Plains tribes were common and the Civil War was particularly devastating for the Cherokee
(Rafferty 1980). The arrival of railroads in the 1870s and 1880s ushered in a new era of trials for
the Cherokee, ultimately leading to unconstrained white settlement of the Cherokee territory and
the end of Cherokee sovereignty in 1898 (McLoughlin 1993).
Site selection
We surveyed much of the Nickel Preserve property and targeted study areas that had preserved
and abundant remnants of shortleaf pine (Pinus echinata). Study site locations also were found
by consulting the managers of the Nickel Preserve for known areas with fire-scarred pine
stumps, snags, and trees. The study sites include one fire history site that had many samples
available and four fire history site clusters where only a few samples were available. The best
site, based on the number of samples and the abundance of fire scars, was located in Tully
Hollow (Figure 1) in an area of approximately 1.2 krrr'. At all sites, we exhaustively collected all
available pine remnants. Four site clusters (Figure 2), areas with concentrated stumps or trees
with fire scars, were used in combination with the Tully Hollow fire history site to determine the
historic extent of fires. The study sites were limited in area as much as possible in order to
estimate mean fire intervals that are unaffected by both scarring rates and site area (Baker and
Ehle 2001).
Sample collection and processing
Shortleaf pine was selectively preferred to other tree species because of the potential for long fire
scar records, the presence of charcoal associated with basal scars, and the sensitivity of the
species to scarring. Samples were selected based on age, wood preservation, and the presence of
scars on live trees. Location (GPS coordinates), slope, and aspect were recorded for each tree
sampled. Cross-sections from live shortleaf pine trees, cut stumps, and natural remnants were
surfaced, measured, and cross-dated. Surfaces of cross-sections were sanded with successively
finer sandpaper (120 to 600 grit). Ring-width series from each sample were plotted and used for
visual cross-dating and signature year identification (Stokes and Smiley 1968). A master dating
chronology was constructed from the tree-ring measurements. The samples and dating
chronology were cross-dated and verified using shortleaf pine chronologies from the Missouri
and Arkansas Ozarks (Guyette 1996; Stambaugh and Guyette 2004). The computer program
COFECHA (Holmes et al. 1986; Grissino-Mayer et al. 1996) was used to ensure the accuracy of
cross-dated tree-ring series.
Fire scars and chronologies
Fire scars were identified by cambial injury, callus tissue, traumatic resin canals, and charcoal.
Fire scars were dated to the year and season of cambial injury. We used the computer program
FHX2 (Grissino-Mayer et al. 1996) to plot composite fire scar chronologies and graphs. We
used SAS/ST AT (2002) software for the statistical summaries, analysis of means, and regression
and correlation analyses. Fire intervals have been described in several ways. Mean fire intervals
(MFIs) are the most often used and are simply the mean of the periods between fire scars (i.e.,
fire events) in years (Dietrich 1980). We averaged the number of fires per decade and created a
time series which was used in correlation analyses with human population density.
Reconstructed drought data
Fire event data were compared to proxy climate data reconstructed from robust regional tree ring
series. The proxy climate data used were reconstructed Palmer Drought Severity Indices (PDSI)
(Cook et al. 2004) averaged for the Ozark region (grid points: 192, 193). All climate data are
available from the Paleoclimate Program of the National Oceanic and Atmospheric
Administration. In the time-series analysis of fire frequency, drought data were smoothed using
a 1O-yr moving average so as to correspond to fires per decade.
Human population density
Human population density is often difficult to estimate in longer term analyses because of
rapidly changing population, area of occupancy, season of residence, and unknown population
sizes. However, this study region has an exceptional record of Native American population
because of its location in Native America, early records of 'land allotments' by treaties (1700-
1900), and descriptions of different tribal groups. During the early period (~1630 to 1780) of
this study's fire scar record the region was occupied by the Osage and others. The Osage
claimed their original territory in what is now northeast Oklahoma, southwest Missouri,
northeast Arkansas and southeast Kansas (Vogt 1974). The Nickel Preserve fire history study
sites were a small area of a large region occupied by the Osage at low population density
(Guyette et al. 2002).
Cherokee migration and population are particularly important to this study because Cherokee
lived in and near the study area for nearly two centuries (Rafferty 1980). Associations of
Cherokee migration and population with fire history data have been documented in several
studies (Guyette and Stambaugh 2005; Guyette et al. 2002; Guyette et al. 2006a). Cherokee
population estimates were derived from the regions of southeast Missouri, later in northwest
Arkansas (Royce 1899; Gilbert 1996), and then in northeast Oklahoma (Morris et al. 1986).
During the winter of 1811-1812 many Cherokee moved from Missouri to Arkansas and their
population in northwest Arkansas (and probably northeast Oklahoma) increased to about 4,500
(Stevens 1991). In 1828, the Cherokee moved further west into the region of northeastern
Oklahoma. Later, in 1838, approximately 13,000 Cherokees were forcefully removed from their
homelands in the eastern United States along the Trail of Tears to northeast Oklahoma that
included the fire history study sites. Using many of these data sources we derived annual
estimates of Cherokee population from decadal historic population estimates. We used decadal
and sub decadallinear interpolation to derive annual population densities of Native America at
the study sites. Interpolations were based on 13 historic estimates of Cherokee and Osage
populations from several data sources (Gilbert 1996, Guyette et al. 2002, Morris et al. 1986,
Rafferty 1980, Royce 1899; Vogt1974).
E. RESULTS:
The fire scar record
Over 324 fire scars on 49 shortleafpine remnant stumps and trees were located, identified, and
dated at the five sites (Figure 2). The majority of sample trees (34) were located at Tully Hollow
and a fire history was developed for this site (Figure 3). At Tully Hollow the mean fire interval
varied from 1.7 to 17 years between 1633 and 1925 (Table 1). Although the period after 1925 is
only represented by two trees at Tully Hollow, there were thousands of un scarred and
uncollected trees at that location that had no recent fire scars. Thus, the long (30 years or less)
intervals during this period are more representative of fire frequency than might be expected
from judging the data based on sample size alone (Figure 2). The percentage of trees scarred in a
single year ranged from 5 to 48. Nearly all (98 percent) fires occurred in the dormant season.
Table 1. Periods of the historic fire regime based on written history and fire frequency. Mean
fire intervals (MFls given in years) were calculated for the entire Nickel Preserve (NP) and for
the smaller extent of Tully Hollow (TLY). MFls for the entire Nickel Preserve are based on the
combined composite fire interval for the five different study sites. Because of low sample sizes
at four of the sites and few sites overall, the mean fire interval statistics for the entire Nickel
Preserve are conservative estimates and likely do not represent all fires within the area. Drought
is the reconstructed PDSI (Cook et al. 2004).
Cultural Period, MFI MFI Weibull Mean % Mean Ethnic Correlation
eras calendar (NP) (TLY) median trees # fires Groups coefficients
years (range) interval scarred, per (drought x
(TLY) (# fires) decade % trees
scarred)
Native 1650-1780 na 5.0 4.45 13.41 (15) 2.0 Osage, -0.211
American (1-17) Wichita,
Caddo
Native 1780-1830 2.2 2.5 2.5 9.5 (21) 4.0 Osage, -0.30*
American (1-4) others
migration I
Native 1830-1889 1.3 1.7 1.6 11.0 (35) 6.3 Cherokee -0.06
American (1-4)
migration II
Euro 1890-1925 1.7 2.2 2.0 19.2 (17) 4.6 Cherokee, -0.01
American (1-4) Euro
settlement American
Fire 1925-1992 5.0 17 16 na 0.5 Euro 0.02
suppression (8-30) American
IDates for this analysis were 1731-1780 because of limited sample numbers before 1731. * = P < 0.05. Study area
sizes are: Tully Hollow (TLY) approximately 121 ha, Nickel Preserve (NP) approximately 6880 ha.
Fire and drought
Three climate-fire associations were found at the study site: 1) fire years were slightly more
common in dry years (Figure 4),2) years with fires oflarge extent were synchronous with
regional droughts, and 3) effects of human ignitions and fuels were more important than annual
climate differences with respect to determining the frequency of most fires between 1680 and
1880. During this period twenty four fire years (34 percent) occurred during wetter than normal
conditions (PDSI > 0), while 47 fire years (66 %) occurred during drier than normal conditions
(PDSI < 0). Widespread fires occurred at the study sites in 1753, 1772, 1780, 1786, 1801 and
1808 during drought years with regional PSDI values that averaged -2.2. Annual reconstructed
drought explained about 10 percent or less of the variance in fire frequency compared to over 80
percent that was explained by fuels and human population density (Equation 1,2,3).
Temporal effects of prior fire on the percent of trees scarred
The number of years since the last fires was an important factor influencing the percent of trees
scarred annually during fire years (Table 2). This change in the percent of trees scarred implies
that some increased degree of fire intensity was caused by a temporal reduction of fuel
accumulation. Our data support this hypothesis and indicate that fuel accumulation for up to
three years before a fire was the most important fuel reduction proxy. Here we used the number
of fire years and the percent of trees scarred during those years as a proxy for fuel removal by
fire. We found a weighted mean of the percent of trees scarred for the three years before a fire
event to be the most significant predictor of the percent of trees scarred. Weights used in
averaging were 1.0 for one year prior, 0.6 for two years prior, and 0.3 for three years prior to the
fire event. Longer time lags were not significant and the weighted averaged follows an expected
exponential decline in fuel accumulation in the region (Stambaugh et al. 2006). Reconstruction
PDSI was tested as a predictor variable in this model but was not significant. The prior fuel
reduction by fire model is described by the regression model (Figure 5):
%TSCAR = l lPe (-0. 112x3ps), Equation 1
where:
%TSCAR = percent of trees scarred at Tully Hollow,
3fs = weighted (1.0, 0.6, 0.3) mean of percent trees scarred in previous 3 years,
r = 0.13, P < 0.01,
Period of record: 1680 to 1880,
Table 2. Correlation coefficients among fires per decade and the percent of trees scarred with
anthropogenic and environmental variables (1680-1880). The Previous Fire Index is a proxy
estimate ofunbumed fuels based on a scaled mean of percent trees scarred in previous 3 years.
Ln is the natural log of population. Statistically significant (p<0.05) tests have an *.
"Significance levels for population density and fire variable correlation coefficients are not given
because of the high autocorrelation in population time series. Knowledge of human- fire-cultural
associations at low population levels gives a priori qualitative and quantitative significance to
these correlations (Guyette et al. 2002, 2006a). b is for the natural log of percent trees scarred
during fire years.
Population and climate variables Fires per decade Percent trees scarred
Population density (Osage+Cherokee) 0.74a o.is'
Ln (population density) (Osage+Cherokee) 0.80a 0.17a
Drought (reconstructed) - 0.06 -0.14*
Drought (reconstructed, % scarred fire years) - 0.02 - 0.33*°
Previous Fire Index 0.34* 0.20*
Fire frequency and human population
The importance of anthropogenic influences on the fire regime was evident in the large
differences in correlations of climate and human variables with fire variables (Tables 1 and 2).
Associations among fire variables (Previous Fire Index, fires per decade) and human population
variables were stronger than with local drought reconstructions (Table 2). By far the most
important variable affecting the early (before 1880) historic record of the fire regime was the
population of Native Americans. Fire frequency (fires per decade) was positively correlated with
population density (Table 2). A regression equation was developed that described the number of
fires per decade from Native American population density (Figure 6):
Fires per decade = 7.7 +1.14(popdensity) Equation 2
where:
Fires per decade = the number of fires per 10 year period at Tully Hollow,
popdensity = natural log of the sum of Osage and Cherokee population per 28,000 krrr',
r2 = 0.75, P <0.001,
period of record: 1680 to 1880,
Although it is difficult to address the statistical significance of these auto correlated series
because of the dependence of these observations (i.e., moving averages and annual population
interpolation), the strength of the correlation between fires per decade and Cherokee population
was robust (r = 0.81) and consistent with similar analyses (Guyette et al. 2002, Guyette et al.
2006a).
Fire frequency human-climate model
Fire frequency at decadal temporal scales can be affected by anthropogenic ignitions and decadal
climate variability. Drought can enhance the probability of burning by decreasing fuel moisture
and increasing the effectiveness of ignitions and fire spread. Drought can also decrease the
probability of burning by reducing fuel production and ignition effectiveness, especially after
burning has reduced fuels. In ignition-saturated environments, fuel production becomes the
limiting factor controlling the frequency of fire (Guyette et al. 2002). There is some support for
these hypotheses in this studies regression modeling results. We predicted fire frequency using
the population density of Native Americans as an ignition proxy and reconstructed drought
(PDSI, Cook et al. 2004) as a fuel production proxy. The resulting equation is:
Fires per decade = 8.08 + 1.42(popdensity) + 0.47(PDSI) Equation 3
where:
Fires per decade = the number of fires per 10 year period at Tully Hollow,
Popdensity = natural log of the sum of Osage and Cherokee population per 28,000 krrr',
PDSI is the 7 year average ofthe reconstructed Palmer Drought Severity Index,
r2 = 0.78, P <0.00, partial r2 are is 0.75 for population and 0.03 for drought,
intercept and variables are significant (p>O.Ol),
period of record: 1680 to 1880.
The interesting aspect of Equation 3 is that when the effects of ignitions (population density) are
taken out in the multiple regression procedure what is left are drought periods that have less
frequent fire (+ sign in front of the PDSI coefficient). A small (~3 percent) but significant
component of the predicted fires per decade is found to decrease with drought and increase with
wetness (Figure 7).
F. DISCUSSION:
The fire scar record
The fire scar record in the Oklahoma Ozarks had similarities to those in the eastern Ozarks of
Arkansas and Missouri. Widespread fires occurred across the Ozarks of Missouri, Arkansas, and
Oklahoma (study area) in 1657,1753,1772,1780,1786,1801,1808. These fires likely
encompassed very large areas, and were likely high intensity, high severity fires that may have
resulted in forest canopy removal. Fires during these years probably resulted from the
interactions of drought, Native American migrations, human conflict, and human attempts to
culture or condition the landscape for subsistence as well as increased accidental fires resulting
from greater human population density.
The pre-Euro-American settlement mean fire interval at the Tully Hollow site was similar to that
of other fire history sites at similar latitudes in North America within oak and pine woodland and
forest ecosystems (Table 3). Although we report mean fire intervals with two significant figures,
it is doubtful, given the limited precision of fire scar history reconstructions, that any ofthe MFIs
in Table 3 are significantly different. Thus, the Tully Hollow MFI is consistent with other
regional fire history site MFls with open forest structure during the period of pre-Euro-American
influence.
Fires were least frequent between about 1925 and 2000 at the Oklahoma Ozark study sites
(Figures 2, 3). Mean fire intervals at the study site during this period are in contrast to other fire
history studies in the adjacent Cross Timbers physiographic region of Oklahoma which were not
reduced in frequency (Clark et al. 2007, DeSantis et al. 2010, and Stambaugh et al. 2009). This
difference in fire frequency could be the result of climate, topography, human population,
vegetation, or burning culture. The drier climate of the Cross Timbers is a major factor in the
decrease in forest cover and the increase in more pyrogenic grasslands. More rapid fire spread in
the less rugged landscapes with more abundant areas of grassland fuels could be a major
contributing factor. Additionally, the culture of burning was changed more in forested regions of
the U.S. by education and propaganda on the results of burning for industrial forestry. In
contrast, a culture of burning persists today in many grassland regions with an agricultural focus
on grazmg.
Table 3. A comparison of the pre Euro American MFI of the Tully Hollow fire regime with
those of forest, woodland, and savanna fire regimes between 34°N and 37°N latitude.
Site name Tully Caney Granny Saltwell Land Wichita
Hollow Mountain Gap Hollow Between Mountains
the Lakes
State East OK SouthMO NorthAR Mid TN WestKY West OK
Period 1650-1830 1702-1821 1680-1820 1700-1810 1700-1810 1720-1820
Vegetation Mixed oak- Mixed oak Mixed oak- Mixed oak Mixed oak Oak-cedar
pine forest, forest, pine forest forest, forest, woodlands
woodland, woodland, woodland woodland woodland pram..e
savanna savanna
Mean fire 5.0 years 5.2 years 4.6 years 6.0 years 6.6 years 6.6 years
interval
Data This study Guyette & Guyette & Guyette & Guyette et Stambaugh
source Cutter Spetich Stambaugh al. 2008 et al., 2009
1991 2003 2005
Fire and climate
Many of the years when fires occurred at the five study sites were the same years that fire
occurred at other fire history sites throughout the Ozark region of Arkansas and Missouri
(Guyette et al. 2006a). The Oklahoma, Arkansas, and Missouri Ozarks fire history data indicate
that there was extensive burning in a 50 year period (1753, 1772, 1780, 1786, 1801, and 1808)
associated with annual drought and anthropogenic ignitions as eastern Native American began
migrating west (Table 4). We estimate that fires between 1748 and 1810 in the Ozarks of
Arkansas, Missouri and Oklahoma could have burned over a total area (as estimated by the
number of sites with fire scars) equal to three times the size of the Ozarks during this 62 year
period (Guyette et al. 2006a). Thus, an area the size of the Ozarks in Arkansas, Missouri, and
Oklahoma (~12,950,000 ha) burned about every 21 years. Since these fires were large and
occurred during known drought years they were probably mixed-severity fires and included
some stand replacement fires. The occurrence of these large mixed-severity fires as well as more
frequent maintenance fires at the study sites probably lead to more open forest canopies in
woodlands.
Major Ozark fire years were associated with widespread drought (Table 4). Low correlations
between mild drought and fire are to be expected because of the timing differences between tree
growth based summer climate reconstructions, and the fire season (fall, winter, early spring) as
documented by dormant season fire injuries. This dormant season regime is expected because of
burning conditions between October and mid- to late-April and when micro-canopy climate
conditions favor burning (lower humidity, higher surface winds, more solar exposure of tree
litter fuels, and dry litter fall).
Table 4. Percent of study sites burned at other Ozark locations during major fire years at
the Nickel Preserve. Rank is by the mean percentage of all sites in the Ozark region
(right hand column). Drought is reconstructed Palmer Drought Severity Index (PDSI) for
the Ozark region (Cook et al. 1999; Cook et al. 2004). More negative PDSI values
indicate increasing drought severity.
Fire Oklahoma Lower Interior Missouri Drought Rank Ozark
Year Ozarks Boston Boston Ozarks (PDSI) region
Mtns. (AR) Mtns. (AR)
1780 40% 100 % 33 % 50% incipient dry, 1 56 %
-0.99
1808 40% 66% 66% 26% near normal, 2 49%
-0.46
1786 20% 66% 66 % 23 % mild drought, 3 44%
-1.14
1772 25 % 100 % 0% 27% extreme 4 38 %
drought, -4.45
1801 40% 0% 66% 31 % extreme 5 34%
drought, -4.33
1753 25 % 0% 66% 39% mild drought, 6 32 %
-1.78
Fire frequency and human population
Threshold values for the effects of human population density on fire frequency represent the
population density at the time when more humans (and ignitions) fail to increase the frequency
of fire (Guyette et al. 2006b). At this point the landscape is saturated with ignitions and fuel
availability becomes the limiting variable affecting fire frequency. The fire regime at the study
site transitioned from an Ignition-dependent stage to a Fuel-limited stage circa 1850 at a human
population density of 0.49 humans per km2 (Guyette et al. 2002). This compares with a threshold
value of 0.64 humans per km2 that was reached in the Missouri Ozarks at the same time by early
Euro-American subsistence settlers. A threshold value of 0.26 (humans per krri') in the interior
Boston Mountains of Arkansas was reached earlier (1820) with increases in Cherokee population
density. Estimates of human populations and their landscape density are coarse and small
differences in threshold values of population density may not be significant. Although
differences in population and topography are known to playa role in fire frequency (Guyette et
al. 2006a, Stambaugh and Guyette 2008) the role of vegetation and climate are unknown for the
study site.
Conclusions and management implications
This study and others indicate that humans have been an important cause in shaping ecosystem
for centuries ifnot millennia (Delcourt and De1court 1997). Humans now and in the past have
used fire to culture this ecosystem for many reasons. The study area is located between two
physiographic provinces (the Ozarks and Cross Timbers), along a major river system, next to a
transportation corridor, and in a fertile stream valley. These characteristics have made the
location attractive to human cultures for centuries if not millennia. Arguably, the continued use
of prescribed fire matches the historical fire regime of this ecosystem.
In the Oklahoma Ozarks, large and probably severe fires that may have altered the forest canopy
occurred about every 21years. Although fire prescriptions to maintain canopy openings are often
effective, severe fire effects are difficult to mimic through fire alone because of the potentially
dangerous fire weather and fuel conditions required. Canopy openings that mimic severe fires
may be duplicated by firing techniques that create locally hot conditions or by silvicultural
treatments. Our results suggest that historically, fuel accumulation for at least three years
resulted in increased fire severity. If management goals are to remove small woody stems while
maintaining open canopies then fire intervals of three years in length may be most effective.
In summary, there were at least five significant findings from this study that may have
management implications.
1. Human population density and culture were the most important factors affecting the
frequency of fire during the three centuries of record. Frequent burning to enhance
ground level vegetation by overs tory canopy removal was repeatedly associated with the
occupancy of the site by Native Americans (Osage, Cherokee, and others) and by the
present owners (The Nature Conservancy). Less frequent burning occurred between
1925 and 2000 that may be associated with cultural changes and industrial forestry.
2. The duration of fuel accumulation was shown to have an effect on fire severity and tree
scarring. Fire severity was increased when there had been no fires (reduced fuel
accumulation) for at least 3 years.
3. Climate appeared to influence the range of variability in the frequency of fire at the study
site owing to two processes: 1) reduced fuel production and fire by decadal droughts, and
2) large scale droughts allowing wide spread severe fires. Annual reconstructed drought
conditions were poor predictors of individual fire years.
4. Prior to 1830, fire frequency in the Oklahoma Ozarks was similar to that found at
woodland-savanna ecosystems populated by Native Americans between 34°N and 37°N
latitude in mid-continental North America.
5. Fires were most frequent between 1830 and 1889 during the highest levels of Cherokee
population and ownership.
Acknowledgments
The authors thank Chris Wilson, manager ofTNC Nickel Preserve, Adam Bale, Joe Marschall,
and Erin McMurry for their enthusiasm and assistance in the field and/or laboratory. We also
would like to thank The Nature Conservancy and the Oklahoma Dept. of Wildlife Conservation
for their technical and funding support.
G. SIGNIFICANT DEVIATIONS: none
H. PREPARED BY: Richard Guyette and Michael Stambaugh
University of Missouri
I. DATE: February 7,2011
J.APPROVEDBY: Ql2lM Q.Jlr Wildlife Divf§ion Ad illiStTation
Oklahoma Department of Wildlife Conservation
K. LITERATURE CITED
Bailey, G. 2010. Traditions of the Osage: stories collected and translated by Francis la Flesche.
University of New Mexico Press: Albuquerque. 176 pp.
Baker, W. L., and Ehle, D. 2001. Uncertainty in surface-fire history: the case of ponderosa pine
forests in the western United States. Canadian Journal of Forest Research 31(7), 1205-
1226.
Burns, L. 2004. A history of the Osage people. University of Alabama Press: Tuscaloosa.
576 pp.
Clark, S.L., Hallgren, S.W., Engle, D.M. and Stahle, D.W. 2007. The historic fire regime on the
edge of the prairie: a case study from the Cross Timbers of Oklahoma. Pages 40-49 in:
R.E. Masters and K.E.M. Galley, editors. Proceedings of the 23rd Tall Timbers Fire
Ecology Conference: Fire in Grassland and Shrubland Ecosystems. Tall Timbers
Research Station, Tallahassee, Florida.
Clark, S., Hallgren, S. W., Lynch, T. B. and Stahle, D. W., 2005. Characteristics of the
Keystone Ancient Forest Preserve, an old-growth forest in the Cross Timbers of
Oklahoma. Natural Areas J. In Press.
Cook, E.R., Meko, D.M., Stahle, D.W., and Cleaveland, M.K., 1999. Drought reconstructions
for the continental United States. Journal of Climate 12: pp. 1145-1162.
Cook, E.R., D.M. Meko, D.W. Stahle, and M.K. Cleaveland. 2004. North American summer
PDSI reconstructions. IGBP PAGES/ World Data Center for Paleoclimatology Data
Contribution Series #2004-045. NOAAlNGDC Paleoclimatology Program, Boulder, CO.
Delcourt, H.R.; Delcourt, P.A. 1997. Pre-Columbian Native American use of fire on Southern
Appalachian landscapes. Conservation Biology. 11(4): 1010-1014.
DeSantis, R.D., Hallgren, S.W., and Stahle, D.W. 2010. Historic fire regime of an upland oak
forest in south-central North America. Fire Ecology 6:45-61. doi:
10.4996/fireecolo gy.0603 045.
Dietrich, J.H. 1980. The composite fire interval- a tool for more accurate interpretation of fire
history. In: Stokes, M.A., and Dieterich, lH. (Tech. Coord.), Proceedings of the Fire
History Workshop. USDA Forest Service General Technical Report RM-81, pp. 8-14.
Gilbert, J. 1996. The Trail of Tears across Missouri. University of Missouri Press, Columbia,
MO. 122 pp.
Goins, C.R. and D. Goble. 2006. Historical atlas of Oklahoma, 4th Edition. University of
Oklahoma Press: Norman. 286 pp.
Goodwin, G.C. 1977. Cherokees in transition: a study of changing culture and environment
prior to 1775. Department of Geography, University of Chicago. Research Paper No.
181. 207pp.
Grissino-Mayer, H.D., Holmes, R.L., and Fritts, H.C. 1996. International Tree-Ring Data Bank
Program Library Version 2.0 user's manual. Laboratory of Tree-Ring Research,
University of Arizona, Tucson, AZ. 106 pp.
Guyette, R.P. 1996. Tree-ring data, Ontario and Missouri. International Tree-Ring Data Bank.
IGBP PAGES/World Data Center for Paleoclimatology, Data Contribution Series# 92-
014. NOAAA NGDC Paleoclimatology Program, Boulder, CO. USA.
Guyette, R.P. and B.E. Cutter. 1991. Tree-ring analysis of fire history of a post oak savanna in
the Missouri Ozarks. Natural Areas Journal 11:93-99.
Guyette, R.P., Muzika, R.M., and Dey, D.C. 2002. Dynamics of an anthropogenic fire regime.
Ecosystems 5: 472-486.
Guyette, R.P., Spetich, M.A. 2003. Fire history in the Lower Boston Mountains. Forest Ecology
and Management 180: 463-474.
Guyette, R.P., Spetich, M.A., and Stambaugh,M.C. 2006. Historic fire regime dynamics and
forcing factors in the Boston Mountains, Arkansas, USA. Forest Ecology and
Management 234: 293-304.
Guyette, R.P., and Stambaugh, M.C. 2005. Historic barrens forest structure and fire regimes
Assessment-Interim Report 2, Arnold Air Force Base, Tullahoma, Tennessee. 121 pp.
Guyette, R.P., Stambaugh, M.C., and Dey, D.C. 2008. Preliminary report on fire history at
Land-Between-The-Lakes. Unpublished Report for Land Between the Lakes National
Recreation Area. Golden Pond, KY.
Guyette, R.P., M.C. Stambaugh, R.M. Muzika, and D.C. Dey. 2006b. Fire scars reveal
variability and dynamics of eastern fire regimes. In: (Dickinson, M. B., ed.) Fire in
eastern oak forests: delivering science to land managers, proceedings of a conference;
2005 November 15-17; Columbus, OH. Gen. Tech. Rep. NRS-P-l. Newtown Square,
PA: U.S. Department of Agriculture, Forest Service, Northern Research Station. 304 pp.
Holmes, R.L., Adams, R., and Fritts, H.C. 1986. Quality control of crossdating and measuring: a
user's manual for program COFECHA. In: Tree-ring Chronologies of Western North
America: California, Eastern Oregon and Northern Great Basin. Laboratory of Tree-Ring
Research, University of Arizona, Tucson, AZ, pp. 41-49.
Jones, B.M. and O.B. Faulk. 1984. Cherokees: an illustrated history. The Five Civilized Tribes
Museum: Muskogee, OK. 176 pp.
Lafon, C. W. 2005. Reconstructing fire history: An exercise in dendrochronology. Journal of
Geography 104:127-137.
McLoughlin, W.G. 1993. After the Trail of Tears: the Cherokees' struggle for sovereignty,
1839-1880. University of North Carolina Press: Chapel Hill. 439 pp.
Morris, lW., Goins, C.R., and McReynolds, E.C. 1986. Historical Atlas of Oklahoma.
University of Oklahoma Press, Norman.
Rafferty, M.D. 1980. The Ozarks land and life. University of Oklahoma Press, Norman. USA
Royce, C.C. (Compiler). 1899. Indian Land Cessions in the United States. In: Eighteenth Annual
Report of the Bureau of American Ethnology, 1896-1897, Part 2. Government Printing
Office, Washington, D.C.
Rudis, Y.A., and Skinner, T'V. 1991. Fire's importance in South Central U.S. forests:
distribution of fire evidence. In: Nodvin, S.C., and Waldrop, T.A., eds. Fire and the
environment: ecological and cultural perspectives: Proceedings of an international
symposium. USDA Forest Service General Technical Report SE-69, pp. 240-251.
SAS/STAT.2002. SAS User's Guide: Statistics, Version, 5th ed. SAS Institute, Cary, NC.
955 pp.
Stambaugh, M.C. and R.P. Guyette. 2008. Predicting spatio-temporal variability in fire return
intervals using a topographic roughness index. Forest Ecology and Management 254:
463-473.
Stambaugh, M.C., and Guyette, R.P. 2004. The long-term growth and climate response of
shortleafpine at the Missouri Ozark Forest Ecosystem Project. In: Yaussy et al., eds.
Proceedings of the 14th Central Hardwoods Conference, Delaware, Ohio. USDA Forest
Service GTR NE-316. pp 448-458.
Stambaugh, M.C., Guyette, R.P., Godfrey, R., McMurry, E.R., and Marschall, lM. 2009. Fire,
drought, and human history near the western terminus of the Cross Timbers, Wichita
Mountains, Oklahoma. Fire Ecology 5:63-77. Doi 10.4996/fireecology.0502051.
Stambaugh, M.C., R.P. Guyette, K. Grabner, and J. Kolaks. 2006. Understanding Ozark forest
litter variability through a synthesis of accumulation rates and fire events. Pages 321-332
In (Butler, B.W and Andrews, P.L., comps) Fuels Management- How To Measure
Success: Conference Proceedings. 2006, 28-30 March; Portland, OR. Proceedings
RMRS-P-41. Fort Collins, CO: U.S. Department of Agriculture, Forest Service, Rocky
Mountain Research Station.
Stevens, D. L. Jr. 1991. A homeland and a hinterland: the Current and Jacks Fork Riverways.
Historic Resource Study, Ozark National Scenic Riverways, National Park Service. Van
Buren, Missouri. 248 pp.
Stokes, M.A., and Smiley, T.L. 1968. Introduction to tree-ring dating. Univ. of Chicago Press,
Chicago, IL. 78 pp.
Vogt, F.W. 1974. Osage Indians I, Osage Research Report, Indian Claims Commission. Garland
Publishing Inc. New York. 371 pp.
Figure 1. Map showing the topography of The Nature Conservancy's Nickel Preserve and the
locations of fire history sites. One fire history site consisting of 34 trees was collected at Tully
Hollow (TUL) whose area is depicted by the dashed line. Other outlying fire history site clusters
were located in Pumpkin Hollow (PMK), Dog Hollow (DOG), Cedar Hollow (CDH), and Tell
Hollow (TEL).
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Figure 2. Composite fire scar history diagram of all five Nickel Preserve sites. Each horizontal
line represents the length of the fire scar record at the collection site. Bold vertical marks
represent fire scars. The preserve-wide composite fire scar chronology (bottom axis) indicates
the presence of a fire at one or more of the study sites.
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Calendaryear
Figure 3. Tully Hollow fire history showing fire scar dates of34 individual trees and a fire scar
composite chronology for the site. Each horizontal line represents the length ofthe fire scar
record of a live shortleaf pine tree or remnant. Each bold vertical mark represents a fire scar on
trees. The composite fire scar chronology with all fire scar dates is shown at the bottom of the
figure.
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1650 1700 750 1800 1850 900 1950 2000
Calendar year
Figure 4. Scatter plot of the percent trees scarred and drought (Palmer Drought Severity Index).
The association of drought on the occurrence of fire and percentage of trees scarred is illustrated
for dry years (negative PDSI values, left side of graph) and wet years (positive PDSI values,
right side of graph). There were 33 fires during wet years (right side of graph) and 42 fires
during dry years. The percent of trees scarred during wet and dry years was not significantly
different.
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Figure 5. Scatter plot and non linear regression line (Equation 1) relating percent trees scarred to
the previous three year weighted mean of the percent tree scarred. The annual percent of trees
scarred serves as a proxy for fire extent and severity (y-axis) while the prior three-year mean of
the percent oftree scarred serves as a proxy for fuel reduction by fire (x-axis).
o o scarring data
40 - regression line
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Prior fires (3 year mean, % trees scarred)
Figure 6. Scatter plot and regression (gray line and text) illustrating the association between
natural log of Native American population density and the number of fires per decade (FPD)
between 1680 and 1860. The top axis gives the non logarithmic population densities per 100
km2.
6
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Native American density (humans/1 00 km2)
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8
FPD = 7.7 + 1.4(/n(pop),
where:
FPD = fires per decade,
In(pop) = log[Native American
population density],
period 1680 to 1880,
~ = 0.75,
00000 0
o o
o
o
-5 -4 -3 -2 -1
Native American density (lnlhumans/km'[)
Figure 7. Time series plots of the number of fires per decade and the fires per decade predicted
by population density and drought model (Equation 3).
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Calendar year

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W 2800.7 F293
T-46-P-1 12/06-12/11 c.1
FINAL PERFORMANCE REPORT
FEDERAL AID GRANT NO. T-46-P-1
USING TREE RING ANALYSIS TO DETERMINE FIRE
HISTORY IN THE OKLAHOMA OZARKS
OKLAHOMA DEPARTMENT OF WILDLIFE CONSERVATION
December 31, 2006 through December 30, 2011
FINAL PERFORMANCE REPORT
State: Oklahoma Grant Number: T-46-P-l
Grant Program: State Wildlife Grants
Grant Name: Using Tree Ring Analysis to Determine Fire History in the Oklahoma Ozarks
Grant Period: December 31,2006 - December 30, 2011
Principal Investigators: Richard P. Guyette, Michael C. Stambaugh, and Rose-Marie Muzika
Department of Forestry, University of Missouri
A. ABSTRACT:
The role of humans in past ecosystem fires has had little quantitative attention. Here, we address
this inadequacy by developing fire histories in northeastern Oklahoma at the Nature
Conservancy's Nickel Preserve from 324 dated fire scars on shortleafpine (Pinus echinata)
remnants and trees. The purpose ofthis study was to provide an understanding of the role of
humans, fuels, and climate in the historic fire regime. Variability in the historic fire regime was
associated with human population, time since last fire, and drought. The population density of
the Cherokee Nation and other Native American groups was significantly correlated (r = 0.84)
with the number of fires per decade between 1680 and 1880. At the Tully Hollow site the mean
fire interval (MFI) was 7.5 years from 1633 to 1731 and 2.8 years from 1732 to 1840. Before
1810, during low population densities of Osage and Caddo, the mean fire interval was 4.2 years.
Coincident with the removal of the Cherokee and other native peoples from the eastern United
States into northeast Oklahoma, the mean fire interval reached 1.8 years in length between 1840
and 1890 in this part of the Cherokee Nation. After 1925 a decrease in fire frequency (MFI = 16
years) occurred until the introduction of prescribed fire by the present owners (The Nature
Conservancy). Previously documented widespread (340 km east-west) fires that occurred during
drought years (1657, 1780, 1786 and 1808) in Missouri and Arkansas also occurred in the
Oklahoma Ozarks. Over all, the occurrence of fires at the study site was weakly associated with
drought years. During decadallength dry periods between 1680 and 1880 fire was less frequent.
Fire severity (as measured by the percent of trees scarred) appeared to be lessened in cases when
fire events were preceded by fires in the previous three years.
B. OBJECTIVE:
To determine the fire history of an oak-pine forest, woodland, and savanna mosaic in the
Oklahoma Ozarks, and to examine the key factors that historically influenced fire regimes in the
region.
C. INTRODUCTION:
Throughout North America the quantitative association of historic fire regimes with anthropo-genic
factors is often limited by the quality of data on Native American populations and to a
lesser extent their many cultures (Delcourt and Delcourt 1997). Rarely are human population
and culture data linked at the same location with long-term fire regime data. The Nature
Conservancy's Nickel Preserve in northeast Oklahoma was part ofthe Cherokee Nation in 1828
and it has a fire history that is strongly linked to human population, culture, and ownership for
over three centuries. Fire history information provides both perspective and baseline data that
are relevant to fire ecology, forest restoration, fuels management, human and ecological history,
and species distributions (Lafon 2005, Rudis and Skinner 1991).
The fire history of Oklahoma's diverse vegetation, landscapes, and people is beginning to be
described by studies conducted with fire-scarred oaks. Case studies using fire scar dates in oak
trees from east central (Clark et al. 2007, DeSantis et al. 2010) and southwestern Oklahoma
(Stambaugh et al. 2009) have begun to described the Cross Timbers region. These studies offer
managers with historic fire frequency information but are not often comparable because of site
differences. High spatial and temporal site variability has been found in fire frequency due to
topography, geographic location, and historic human occupancy. No previous-documented fire
histories are known to exist in the western Ozark Highlands region of Oklahoma. The nearest
Ozark fire histories are about 200 km east in higher, cooler, and wetter mountain environments
in northern Arkansas (Guyette et al. 2006). This study describes the historic fire regime in what
is now The Nature Conservancy's (TNC) Nickel Preserve in Cherokee County, Oklahoma by
using fire locations and dates as identified on fire-scarred remnants and trees.
D. APPROACH AND METHODS:
Study location
Study sites are located at what is presently the IT. Nickel Family Nature and Wildlife Preserve,
which occurs on the lands that were occupied by Native American tribes, and were assigned by
treaty to the Cherokee Nation in the decades before 1887 (Figure 1). The 6,880 ha preserve,
owned and managed by TNC since 2000, lies in the Cookson Hills of northeastern Oklahoma
and is bordered by the Illinois River to the west. The region lies on the western edge of the
Ozark Highlands with the lands further west occurring in the Cross Timbers physiographic
region (Clark et al. 2005). The climate is humid continental, with mean maximum temperatures
of22 "C and mean annual precipitation of 122 em. The topography is rugged and dissected, with
steep cherty slopes, ridges, and narrow valleys. Twenty to fifty percent of the region has slopes
over 14 percent (Rafferty 1980). Plant community associations include mixed oak-hickory
(Quercus sp.-Carya sp.) forests, mixed oak-pine (Quercus sp.-Pinus echinata Mill.) woodlands
and savannas, and small prairies.
Human history
The study site region has been continually occupied by humans throughout the period of the fire
scar record. During the early period (~1630-1830) of the fire scar record, the region was likely
occupied by the Osage and Caddo Native American groups (Vogt 1974). As early as 1541, the
study site was within the boundaries of the expanding Osage territory (Bums 2004) and other
Native American groups had left the region by the latter half of the is" century (Vogt 1974;
Bailey 2010). Osage villages were concentrated primarily in the Missouri and Arkansas Ozarks,
but they utilized the western plains portion of their territory for annual game and bison hunts.
The Illinois River trail was one of two significant trails utilized by the Osage for travelling from
Arkansas to Oklahoma hunting grounds (Bums 2004) that bordered the study site.
The Cherokees began migration and cultural change early (before 1775) in the east (Goodwin
1977). By 1817, the "Western Cherokees" that had been settling in Arkansas since the 1790s
were venturing into northeastern Oklahoma, encountering resistance from the Osage. Conflicts
continued between the two tribes through 1825 (Goins and Goble 2006). In 1828, a treaty led to
the exchange of Cherokee lands in Arkansas for land in Indian Territory encompassing the study
site after which the region was occupied primarily by Cherokee for more than 6 decades.
Between 1829 and 1838, the Western Cherokees were occupied with building cabins, clearing
land for cultivation, raising livestock and hunting bison (Jones and Faulk 1984). In 1838, most
of the remaining Eastern Cherokees were forced to relocate to northeastern Oklahoma on what
came to be known as the Trail of Tears. Approximately 5,000 Cherokee were already living in
lands west of the Mississippi when about 14,000 surviving emigrants from the East arrived
(McLoughlin 1993; Goins and Goble 2006).
Many emigrants arrived in the new territory destitute, and struggled to survive in an unfamiliar
climate and environment (McLoughlin 1993). The decades following the arrival of the Eastern
Cherokees were marked by much turmoil as the reunited tribe struggled to establish social,
economic and political stability (McLoughlin 1993; Goins and Goble 2006). Conflicts with
other Plains tribes were common and the Civil War was particularly devastating for the Cherokee
(Rafferty 1980). The arrival of railroads in the 1870s and 1880s ushered in a new era of trials for
the Cherokee, ultimately leading to unconstrained white settlement of the Cherokee territory and
the end of Cherokee sovereignty in 1898 (McLoughlin 1993).
Site selection
We surveyed much of the Nickel Preserve property and targeted study areas that had preserved
and abundant remnants of shortleaf pine (Pinus echinata). Study site locations also were found
by consulting the managers of the Nickel Preserve for known areas with fire-scarred pine
stumps, snags, and trees. The study sites include one fire history site that had many samples
available and four fire history site clusters where only a few samples were available. The best
site, based on the number of samples and the abundance of fire scars, was located in Tully
Hollow (Figure 1) in an area of approximately 1.2 krrr'. At all sites, we exhaustively collected all
available pine remnants. Four site clusters (Figure 2), areas with concentrated stumps or trees
with fire scars, were used in combination with the Tully Hollow fire history site to determine the
historic extent of fires. The study sites were limited in area as much as possible in order to
estimate mean fire intervals that are unaffected by both scarring rates and site area (Baker and
Ehle 2001).
Sample collection and processing
Shortleaf pine was selectively preferred to other tree species because of the potential for long fire
scar records, the presence of charcoal associated with basal scars, and the sensitivity of the
species to scarring. Samples were selected based on age, wood preservation, and the presence of
scars on live trees. Location (GPS coordinates), slope, and aspect were recorded for each tree
sampled. Cross-sections from live shortleaf pine trees, cut stumps, and natural remnants were
surfaced, measured, and cross-dated. Surfaces of cross-sections were sanded with successively
finer sandpaper (120 to 600 grit). Ring-width series from each sample were plotted and used for
visual cross-dating and signature year identification (Stokes and Smiley 1968). A master dating
chronology was constructed from the tree-ring measurements. The samples and dating
chronology were cross-dated and verified using shortleaf pine chronologies from the Missouri
and Arkansas Ozarks (Guyette 1996; Stambaugh and Guyette 2004). The computer program
COFECHA (Holmes et al. 1986; Grissino-Mayer et al. 1996) was used to ensure the accuracy of
cross-dated tree-ring series.
Fire scars and chronologies
Fire scars were identified by cambial injury, callus tissue, traumatic resin canals, and charcoal.
Fire scars were dated to the year and season of cambial injury. We used the computer program
FHX2 (Grissino-Mayer et al. 1996) to plot composite fire scar chronologies and graphs. We
used SAS/ST AT (2002) software for the statistical summaries, analysis of means, and regression
and correlation analyses. Fire intervals have been described in several ways. Mean fire intervals
(MFIs) are the most often used and are simply the mean of the periods between fire scars (i.e.,
fire events) in years (Dietrich 1980). We averaged the number of fires per decade and created a
time series which was used in correlation analyses with human population density.
Reconstructed drought data
Fire event data were compared to proxy climate data reconstructed from robust regional tree ring
series. The proxy climate data used were reconstructed Palmer Drought Severity Indices (PDSI)
(Cook et al. 2004) averaged for the Ozark region (grid points: 192, 193). All climate data are
available from the Paleoclimate Program of the National Oceanic and Atmospheric
Administration. In the time-series analysis of fire frequency, drought data were smoothed using
a 1O-yr moving average so as to correspond to fires per decade.
Human population density
Human population density is often difficult to estimate in longer term analyses because of
rapidly changing population, area of occupancy, season of residence, and unknown population
sizes. However, this study region has an exceptional record of Native American population
because of its location in Native America, early records of 'land allotments' by treaties (1700-
1900), and descriptions of different tribal groups. During the early period (~1630 to 1780) of
this study's fire scar record the region was occupied by the Osage and others. The Osage
claimed their original territory in what is now northeast Oklahoma, southwest Missouri,
northeast Arkansas and southeast Kansas (Vogt 1974). The Nickel Preserve fire history study
sites were a small area of a large region occupied by the Osage at low population density
(Guyette et al. 2002).
Cherokee migration and population are particularly important to this study because Cherokee
lived in and near the study area for nearly two centuries (Rafferty 1980). Associations of
Cherokee migration and population with fire history data have been documented in several
studies (Guyette and Stambaugh 2005; Guyette et al. 2002; Guyette et al. 2006a). Cherokee
population estimates were derived from the regions of southeast Missouri, later in northwest
Arkansas (Royce 1899; Gilbert 1996), and then in northeast Oklahoma (Morris et al. 1986).
During the winter of 1811-1812 many Cherokee moved from Missouri to Arkansas and their
population in northwest Arkansas (and probably northeast Oklahoma) increased to about 4,500
(Stevens 1991). In 1828, the Cherokee moved further west into the region of northeastern
Oklahoma. Later, in 1838, approximately 13,000 Cherokees were forcefully removed from their
homelands in the eastern United States along the Trail of Tears to northeast Oklahoma that
included the fire history study sites. Using many of these data sources we derived annual
estimates of Cherokee population from decadal historic population estimates. We used decadal
and sub decadallinear interpolation to derive annual population densities of Native America at
the study sites. Interpolations were based on 13 historic estimates of Cherokee and Osage
populations from several data sources (Gilbert 1996, Guyette et al. 2002, Morris et al. 1986,
Rafferty 1980, Royce 1899; Vogt1974).
E. RESULTS:
The fire scar record
Over 324 fire scars on 49 shortleafpine remnant stumps and trees were located, identified, and
dated at the five sites (Figure 2). The majority of sample trees (34) were located at Tully Hollow
and a fire history was developed for this site (Figure 3). At Tully Hollow the mean fire interval
varied from 1.7 to 17 years between 1633 and 1925 (Table 1). Although the period after 1925 is
only represented by two trees at Tully Hollow, there were thousands of un scarred and
uncollected trees at that location that had no recent fire scars. Thus, the long (30 years or less)
intervals during this period are more representative of fire frequency than might be expected
from judging the data based on sample size alone (Figure 2). The percentage of trees scarred in a
single year ranged from 5 to 48. Nearly all (98 percent) fires occurred in the dormant season.
Table 1. Periods of the historic fire regime based on written history and fire frequency. Mean
fire intervals (MFls given in years) were calculated for the entire Nickel Preserve (NP) and for
the smaller extent of Tully Hollow (TLY). MFls for the entire Nickel Preserve are based on the
combined composite fire interval for the five different study sites. Because of low sample sizes
at four of the sites and few sites overall, the mean fire interval statistics for the entire Nickel
Preserve are conservative estimates and likely do not represent all fires within the area. Drought
is the reconstructed PDSI (Cook et al. 2004).
Cultural Period, MFI MFI Weibull Mean % Mean Ethnic Correlation
eras calendar (NP) (TLY) median trees # fires Groups coefficients
years (range) interval scarred, per (drought x
(TLY) (# fires) decade % trees
scarred)
Native 1650-1780 na 5.0 4.45 13.41 (15) 2.0 Osage, -0.211
American (1-17) Wichita,
Caddo
Native 1780-1830 2.2 2.5 2.5 9.5 (21) 4.0 Osage, -0.30*
American (1-4) others
migration I
Native 1830-1889 1.3 1.7 1.6 11.0 (35) 6.3 Cherokee -0.06
American (1-4)
migration II
Euro 1890-1925 1.7 2.2 2.0 19.2 (17) 4.6 Cherokee, -0.01
American (1-4) Euro
settlement American
Fire 1925-1992 5.0 17 16 na 0.5 Euro 0.02
suppression (8-30) American
IDates for this analysis were 1731-1780 because of limited sample numbers before 1731. * = P < 0.05. Study area
sizes are: Tully Hollow (TLY) approximately 121 ha, Nickel Preserve (NP) approximately 6880 ha.
Fire and drought
Three climate-fire associations were found at the study site: 1) fire years were slightly more
common in dry years (Figure 4),2) years with fires oflarge extent were synchronous with
regional droughts, and 3) effects of human ignitions and fuels were more important than annual
climate differences with respect to determining the frequency of most fires between 1680 and
1880. During this period twenty four fire years (34 percent) occurred during wetter than normal
conditions (PDSI > 0), while 47 fire years (66 %) occurred during drier than normal conditions
(PDSI < 0). Widespread fires occurred at the study sites in 1753, 1772, 1780, 1786, 1801 and
1808 during drought years with regional PSDI values that averaged -2.2. Annual reconstructed
drought explained about 10 percent or less of the variance in fire frequency compared to over 80
percent that was explained by fuels and human population density (Equation 1,2,3).
Temporal effects of prior fire on the percent of trees scarred
The number of years since the last fires was an important factor influencing the percent of trees
scarred annually during fire years (Table 2). This change in the percent of trees scarred implies
that some increased degree of fire intensity was caused by a temporal reduction of fuel
accumulation. Our data support this hypothesis and indicate that fuel accumulation for up to
three years before a fire was the most important fuel reduction proxy. Here we used the number
of fire years and the percent of trees scarred during those years as a proxy for fuel removal by
fire. We found a weighted mean of the percent of trees scarred for the three years before a fire
event to be the most significant predictor of the percent of trees scarred. Weights used in
averaging were 1.0 for one year prior, 0.6 for two years prior, and 0.3 for three years prior to the
fire event. Longer time lags were not significant and the weighted averaged follows an expected
exponential decline in fuel accumulation in the region (Stambaugh et al. 2006). Reconstruction
PDSI was tested as a predictor variable in this model but was not significant. The prior fuel
reduction by fire model is described by the regression model (Figure 5):
%TSCAR = l lPe (-0. 112x3ps), Equation 1
where:
%TSCAR = percent of trees scarred at Tully Hollow,
3fs = weighted (1.0, 0.6, 0.3) mean of percent trees scarred in previous 3 years,
r = 0.13, P < 0.01,
Period of record: 1680 to 1880,
Table 2. Correlation coefficients among fires per decade and the percent of trees scarred with
anthropogenic and environmental variables (1680-1880). The Previous Fire Index is a proxy
estimate ofunbumed fuels based on a scaled mean of percent trees scarred in previous 3 years.
Ln is the natural log of population. Statistically significant (p<0.05) tests have an *.
"Significance levels for population density and fire variable correlation coefficients are not given
because of the high autocorrelation in population time series. Knowledge of human- fire-cultural
associations at low population levels gives a priori qualitative and quantitative significance to
these correlations (Guyette et al. 2002, 2006a). b is for the natural log of percent trees scarred
during fire years.
Population and climate variables Fires per decade Percent trees scarred
Population density (Osage+Cherokee) 0.74a o.is'
Ln (population density) (Osage+Cherokee) 0.80a 0.17a
Drought (reconstructed) - 0.06 -0.14*
Drought (reconstructed, % scarred fire years) - 0.02 - 0.33*°
Previous Fire Index 0.34* 0.20*
Fire frequency and human population
The importance of anthropogenic influences on the fire regime was evident in the large
differences in correlations of climate and human variables with fire variables (Tables 1 and 2).
Associations among fire variables (Previous Fire Index, fires per decade) and human population
variables were stronger than with local drought reconstructions (Table 2). By far the most
important variable affecting the early (before 1880) historic record of the fire regime was the
population of Native Americans. Fire frequency (fires per decade) was positively correlated with
population density (Table 2). A regression equation was developed that described the number of
fires per decade from Native American population density (Figure 6):
Fires per decade = 7.7 +1.14(popdensity) Equation 2
where:
Fires per decade = the number of fires per 10 year period at Tully Hollow,
popdensity = natural log of the sum of Osage and Cherokee population per 28,000 krrr',
r2 = 0.75, P <0.001,
period of record: 1680 to 1880,
Although it is difficult to address the statistical significance of these auto correlated series
because of the dependence of these observations (i.e., moving averages and annual population
interpolation), the strength of the correlation between fires per decade and Cherokee population
was robust (r = 0.81) and consistent with similar analyses (Guyette et al. 2002, Guyette et al.
2006a).
Fire frequency human-climate model
Fire frequency at decadal temporal scales can be affected by anthropogenic ignitions and decadal
climate variability. Drought can enhance the probability of burning by decreasing fuel moisture
and increasing the effectiveness of ignitions and fire spread. Drought can also decrease the
probability of burning by reducing fuel production and ignition effectiveness, especially after
burning has reduced fuels. In ignition-saturated environments, fuel production becomes the
limiting factor controlling the frequency of fire (Guyette et al. 2002). There is some support for
these hypotheses in this studies regression modeling results. We predicted fire frequency using
the population density of Native Americans as an ignition proxy and reconstructed drought
(PDSI, Cook et al. 2004) as a fuel production proxy. The resulting equation is:
Fires per decade = 8.08 + 1.42(popdensity) + 0.47(PDSI) Equation 3
where:
Fires per decade = the number of fires per 10 year period at Tully Hollow,
Popdensity = natural log of the sum of Osage and Cherokee population per 28,000 krrr',
PDSI is the 7 year average ofthe reconstructed Palmer Drought Severity Index,
r2 = 0.78, P <0.00, partial r2 are is 0.75 for population and 0.03 for drought,
intercept and variables are significant (p>O.Ol),
period of record: 1680 to 1880.
The interesting aspect of Equation 3 is that when the effects of ignitions (population density) are
taken out in the multiple regression procedure what is left are drought periods that have less
frequent fire (+ sign in front of the PDSI coefficient). A small (~3 percent) but significant
component of the predicted fires per decade is found to decrease with drought and increase with
wetness (Figure 7).
F. DISCUSSION:
The fire scar record
The fire scar record in the Oklahoma Ozarks had similarities to those in the eastern Ozarks of
Arkansas and Missouri. Widespread fires occurred across the Ozarks of Missouri, Arkansas, and
Oklahoma (study area) in 1657,1753,1772,1780,1786,1801,1808. These fires likely
encompassed very large areas, and were likely high intensity, high severity fires that may have
resulted in forest canopy removal. Fires during these years probably resulted from the
interactions of drought, Native American migrations, human conflict, and human attempts to
culture or condition the landscape for subsistence as well as increased accidental fires resulting
from greater human population density.
The pre-Euro-American settlement mean fire interval at the Tully Hollow site was similar to that
of other fire history sites at similar latitudes in North America within oak and pine woodland and
forest ecosystems (Table 3). Although we report mean fire intervals with two significant figures,
it is doubtful, given the limited precision of fire scar history reconstructions, that any ofthe MFIs
in Table 3 are significantly different. Thus, the Tully Hollow MFI is consistent with other
regional fire history site MFls with open forest structure during the period of pre-Euro-American
influence.
Fires were least frequent between about 1925 and 2000 at the Oklahoma Ozark study sites
(Figures 2, 3). Mean fire intervals at the study site during this period are in contrast to other fire
history studies in the adjacent Cross Timbers physiographic region of Oklahoma which were not
reduced in frequency (Clark et al. 2007, DeSantis et al. 2010, and Stambaugh et al. 2009). This
difference in fire frequency could be the result of climate, topography, human population,
vegetation, or burning culture. The drier climate of the Cross Timbers is a major factor in the
decrease in forest cover and the increase in more pyrogenic grasslands. More rapid fire spread in
the less rugged landscapes with more abundant areas of grassland fuels could be a major
contributing factor. Additionally, the culture of burning was changed more in forested regions of
the U.S. by education and propaganda on the results of burning for industrial forestry. In
contrast, a culture of burning persists today in many grassland regions with an agricultural focus
on grazmg.
Table 3. A comparison of the pre Euro American MFI of the Tully Hollow fire regime with
those of forest, woodland, and savanna fire regimes between 34°N and 37°N latitude.
Site name Tully Caney Granny Saltwell Land Wichita
Hollow Mountain Gap Hollow Between Mountains
the Lakes
State East OK SouthMO NorthAR Mid TN WestKY West OK
Period 1650-1830 1702-1821 1680-1820 1700-1810 1700-1810 1720-1820
Vegetation Mixed oak- Mixed oak Mixed oak- Mixed oak Mixed oak Oak-cedar
pine forest, forest, pine forest forest, forest, woodlands
woodland, woodland, woodland woodland woodland pram..e
savanna savanna
Mean fire 5.0 years 5.2 years 4.6 years 6.0 years 6.6 years 6.6 years
interval
Data This study Guyette & Guyette & Guyette & Guyette et Stambaugh
source Cutter Spetich Stambaugh al. 2008 et al., 2009
1991 2003 2005
Fire and climate
Many of the years when fires occurred at the five study sites were the same years that fire
occurred at other fire history sites throughout the Ozark region of Arkansas and Missouri
(Guyette et al. 2006a). The Oklahoma, Arkansas, and Missouri Ozarks fire history data indicate
that there was extensive burning in a 50 year period (1753, 1772, 1780, 1786, 1801, and 1808)
associated with annual drought and anthropogenic ignitions as eastern Native American began
migrating west (Table 4). We estimate that fires between 1748 and 1810 in the Ozarks of
Arkansas, Missouri and Oklahoma could have burned over a total area (as estimated by the
number of sites with fire scars) equal to three times the size of the Ozarks during this 62 year
period (Guyette et al. 2006a). Thus, an area the size of the Ozarks in Arkansas, Missouri, and
Oklahoma (~12,950,000 ha) burned about every 21 years. Since these fires were large and
occurred during known drought years they were probably mixed-severity fires and included
some stand replacement fires. The occurrence of these large mixed-severity fires as well as more
frequent maintenance fires at the study sites probably lead to more open forest canopies in
woodlands.
Major Ozark fire years were associated with widespread drought (Table 4). Low correlations
between mild drought and fire are to be expected because of the timing differences between tree
growth based summer climate reconstructions, and the fire season (fall, winter, early spring) as
documented by dormant season fire injuries. This dormant season regime is expected because of
burning conditions between October and mid- to late-April and when micro-canopy climate
conditions favor burning (lower humidity, higher surface winds, more solar exposure of tree
litter fuels, and dry litter fall).
Table 4. Percent of study sites burned at other Ozark locations during major fire years at
the Nickel Preserve. Rank is by the mean percentage of all sites in the Ozark region
(right hand column). Drought is reconstructed Palmer Drought Severity Index (PDSI) for
the Ozark region (Cook et al. 1999; Cook et al. 2004). More negative PDSI values
indicate increasing drought severity.
Fire Oklahoma Lower Interior Missouri Drought Rank Ozark
Year Ozarks Boston Boston Ozarks (PDSI) region
Mtns. (AR) Mtns. (AR)
1780 40% 100 % 33 % 50% incipient dry, 1 56 %
-0.99
1808 40% 66% 66% 26% near normal, 2 49%
-0.46
1786 20% 66% 66 % 23 % mild drought, 3 44%
-1.14
1772 25 % 100 % 0% 27% extreme 4 38 %
drought, -4.45
1801 40% 0% 66% 31 % extreme 5 34%
drought, -4.33
1753 25 % 0% 66% 39% mild drought, 6 32 %
-1.78
Fire frequency and human population
Threshold values for the effects of human population density on fire frequency represent the
population density at the time when more humans (and ignitions) fail to increase the frequency
of fire (Guyette et al. 2006b). At this point the landscape is saturated with ignitions and fuel
availability becomes the limiting variable affecting fire frequency. The fire regime at the study
site transitioned from an Ignition-dependent stage to a Fuel-limited stage circa 1850 at a human
population density of 0.49 humans per km2 (Guyette et al. 2002). This compares with a threshold
value of 0.64 humans per km2 that was reached in the Missouri Ozarks at the same time by early
Euro-American subsistence settlers. A threshold value of 0.26 (humans per krri') in the interior
Boston Mountains of Arkansas was reached earlier (1820) with increases in Cherokee population
density. Estimates of human populations and their landscape density are coarse and small
differences in threshold values of population density may not be significant. Although
differences in population and topography are known to playa role in fire frequency (Guyette et
al. 2006a, Stambaugh and Guyette 2008) the role of vegetation and climate are unknown for the
study site.
Conclusions and management implications
This study and others indicate that humans have been an important cause in shaping ecosystem
for centuries ifnot millennia (Delcourt and De1court 1997). Humans now and in the past have
used fire to culture this ecosystem for many reasons. The study area is located between two
physiographic provinces (the Ozarks and Cross Timbers), along a major river system, next to a
transportation corridor, and in a fertile stream valley. These characteristics have made the
location attractive to human cultures for centuries if not millennia. Arguably, the continued use
of prescribed fire matches the historical fire regime of this ecosystem.
In the Oklahoma Ozarks, large and probably severe fires that may have altered the forest canopy
occurred about every 21years. Although fire prescriptions to maintain canopy openings are often
effective, severe fire effects are difficult to mimic through fire alone because of the potentially
dangerous fire weather and fuel conditions required. Canopy openings that mimic severe fires
may be duplicated by firing techniques that create locally hot conditions or by silvicultural
treatments. Our results suggest that historically, fuel accumulation for at least three years
resulted in increased fire severity. If management goals are to remove small woody stems while
maintaining open canopies then fire intervals of three years in length may be most effective.
In summary, there were at least five significant findings from this study that may have
management implications.
1. Human population density and culture were the most important factors affecting the
frequency of fire during the three centuries of record. Frequent burning to enhance
ground level vegetation by overs tory canopy removal was repeatedly associated with the
occupancy of the site by Native Americans (Osage, Cherokee, and others) and by the
present owners (The Nature Conservancy). Less frequent burning occurred between
1925 and 2000 that may be associated with cultural changes and industrial forestry.
2. The duration of fuel accumulation was shown to have an effect on fire severity and tree
scarring. Fire severity was increased when there had been no fires (reduced fuel
accumulation) for at least 3 years.
3. Climate appeared to influence the range of variability in the frequency of fire at the study
site owing to two processes: 1) reduced fuel production and fire by decadal droughts, and
2) large scale droughts allowing wide spread severe fires. Annual reconstructed drought
conditions were poor predictors of individual fire years.
4. Prior to 1830, fire frequency in the Oklahoma Ozarks was similar to that found at
woodland-savanna ecosystems populated by Native Americans between 34°N and 37°N
latitude in mid-continental North America.
5. Fires were most frequent between 1830 and 1889 during the highest levels of Cherokee
population and ownership.
Acknowledgments
The authors thank Chris Wilson, manager ofTNC Nickel Preserve, Adam Bale, Joe Marschall,
and Erin McMurry for their enthusiasm and assistance in the field and/or laboratory. We also
would like to thank The Nature Conservancy and the Oklahoma Dept. of Wildlife Conservation
for their technical and funding support.
G. SIGNIFICANT DEVIATIONS: none
H. PREPARED BY: Richard Guyette and Michael Stambaugh
University of Missouri
I. DATE: February 7,2011
J.APPROVEDBY: Ql2lM Q.Jlr Wildlife Divf§ion Ad illiStTation
Oklahoma Department of Wildlife Conservation
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Figure 1. Map showing the topography of The Nature Conservancy's Nickel Preserve and the
locations of fire history sites. One fire history site consisting of 34 trees was collected at Tully
Hollow (TUL) whose area is depicted by the dashed line. Other outlying fire history site clusters
were located in Pumpkin Hollow (PMK), Dog Hollow (DOG), Cedar Hollow (CDH), and Tell
Hollow (TEL).
N ""\ L~
,~
CJprese~~, B,6tJndary
, ?~ ./\., ..•. -_~-'.c. o 1 2 "4·'"
.3 '- km
Gontou(interval = 20m
Figure 2. Composite fire scar history diagram of all five Nickel Preserve sites. Each horizontal
line represents the length of the fire scar record at the collection site. Bold vertical marks
represent fire scars. The preserve-wide composite fire scar chronology (bottom axis) indicates
the presence of a fire at one or more of the study sites.
I IIII I III II .111111 I till I I I ITEL
I III I I III 1111 II I I' CDH
",---/-+-1 +-1 -tl- I II I " I I III111I u- PMK
--t-----t--I II I 11111" I I I II H :,DOG
11111111111111I11II1I'1" 1111I111111111111111I1111 ItiH 111I I I t ~ TL Y ;)JJ~JJl"~J~/'i~" :.'.~l~~i-U~ ~;
I I I II I III III II
1650 1700 1750 800 1850 900 950 2000
Calendaryear
Figure 3. Tully Hollow fire history showing fire scar dates of34 individual trees and a fire scar
composite chronology for the site. Each horizontal line represents the length ofthe fire scar
record of a live shortleaf pine tree or remnant. Each bold vertical mark represents a fire scar on
trees. The composite fire scar chronology with all fire scar dates is shown at the bottom of the
figure.
L-----:------lf:---+----II~; "'1'012
,+1:---1-111'1'I 1I\ I I, I" ~ " ~llYG~32 g~~ "HIT-,- T Y025 IH.-H:p. Tt'J'019
"'--- , -.-. I II " IlYGZ7
_ TlYGiO
IJ+I--------IIHII----" lLY0;34
l-r------t----' RY028 1+11 ~ Tn020 L)-----+----HII±m..:+...:He-fHH+" I, fir nm.0'13'0005
~+--t.--H-~-I-I-~---------' -tllt-I----', TTLLYYO03O6t.
lLYOO2
[ H L 11--t---+---t-_-f--j,TlYOtt.
1 H-I-l--+t+I-+-H'. - 1LY04 7
TLYOll
TLY008
TLY037
TLY006
11'1'009
TLY033
TLY007
1LY039
rLYOl5
TLYOO3
I l--------~I_~---~ I II
I 't-U-:I-_ - t--I--'
1+4 (I --H-I'I------- I I I H-H+=IIII'I III IH+m-HH-I+-+----+__>
,
; !
,
i
1650 1700 750 1800 1850 900 1950 2000
Calendar year
Figure 4. Scatter plot of the percent trees scarred and drought (Palmer Drought Severity Index).
The association of drought on the occurrence of fire and percentage of trees scarred is illustrated
for dry years (negative PDSI values, left side of graph) and wet years (positive PDSI values,
right side of graph). There were 33 fires during wet years (right side of graph) and 42 fires
during dry years. The percent of trees scarred during wet and dry years was not significantly
different.
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